In recent years, tightening of emission control of carbon dioxide and concern about depletion of fossil fuel demand improvements of fuel consumption (fuel consumption rate) of internal combustion engines. Thus, efforts to improve fuel consumption by reducing various losses of an internal combustion engine are under way. In general, when losses are reduced, the power output necessary for operation of an engine can be reduced so that the minimum power output of the internal combustion engine can be reduced. In such an internal combustion engine, it becomes necessary to control and supply up to a small amount of fuel corresponding to the minimum power output.
Also in recent years, a downsizing engine which reduces the size thereof by reducing the displacement and also obtains power output by a supercharger has attracted attention. The downsizing engine can reduce pumping losses and friction by reducing the displacement so that fuel consumption can be improved. On the other hand, by using a supercharger, sufficient power output can be obtained and also fuel consumption can be improved by inhibiting the degradation of the compression ratio accompanying supercharging thanks to an inlet air cooling effect by cylinder direct injection of fuel. It is necessary particularly for a fuel injection device used for the downsizing engine to be able to inject fuel in a wide range from the minimum injection quantity corresponding to the minimum power output due to a lower displacement to the maximum injection quantity corresponding to the maximum power output obtained by supercharging and an extended control range of the fuel quantity is demanded.
Also, with tightening of emission control, the inhibition of the total quantity of particulate matter (PM) during mode traveling and the particulate number (PN) as the number thereof of an engine are demanded and a fuel injection device capable of controlling a minute injection quantity is demanded. As a means of inhibiting generation of particulate matter, as described in, for example, PTL 1, it is effective to divide a spray during one intake and exhaust stroke into a plurality of times and inject (hereinafter, called divided injection). By performing divided injection, adhesion of fuel to the piston wall surface can be inhibited and thus, injected fuel is more likely to be vaporized and the total quantity of particulate matter and the particulate number as the number thereof can be inhibited. In an engine that performs divided injection, it is necessary to divide fuel to be injected at a time in the past into that to be injected a plurality of times and inject and thus, a fuel injection device needs to be able to control an injection quantity more minute than in the past.
In general, the injection quantity a fuel injection device is controlled by the pulse width of an injection pulse output from an engine control unit (ECU). The injection quantity increases with an increasing injection pulse width and decreases with a decreasing injection pulse width and the relationship thereof is substantially linear. However, the time needed for a needle to reach a valve closed position after the injection pulse is stopped varies due to a rebound phenomenon (bound behavior of the needle) that occurs when the needle collides against a fixed core or a stopper that regulates a displacement of the needle in a region where the injection pulse width is short, posing a problem that the injection quantity does not change linearly with respect to the injection pulse width and thus, a controllable minimum injection quantity of the fuel injection device increases. Also due to the rebound phenomenon of the needle, the injection quantity may not be stable from fuel injection device to fuel injection device and it is unavoidable to set an individual fuel injection device with the largest injection quantity as the controllable minimum injection quantity, leading to an increased minimum injection quantity. If the injection pulse width is further shortened from an injection pulse in a nonlinear region where the relationship between the injection pulse and the injection quantity is not linear, the region becomes a region where the needle and the fixed core do not collide, that is, an intermediate lift region where a valve body is not fully lifted. In such an intermediate lift region, even if the same injection pulse is supplied to the fuel injection device of each cylinder, the lift quantity of the fuel injection device differs immensely due to individual differences arising under the influence of dimensional tolerance, aging and the like of the fuel injection device. Then, the required injection quantity is small in an intermediate lift region and the influence of individual variations of the injection quantity on injection quantity errors becomes pronounced, which makes it difficult to use the intermediate lift region from the viewpoint of stable combustion.
As described above, it is necessary to reduce variations of the injection quantity of a fuel injection device and a controllable minimum injection quantity for the purpose of improving fuel consumption and inhibiting particulate matter and to achieve a significant reduction of the minimum injection quantity, controlling a short injection pulse region having variation characteristics in which the relationship between the injection pulse width and the injection quantity varies individually and the injection quantity in an intermediate lift region where the injection pulse is small and the valve body does not reach the target lift is demanded. To reduce variations of the injection quantity and the minimum injection quantity, it is necessary to be able to detect variations of a valve operation or variations of the injection quantity such as variations in time after an injection pulse generated by the bound phenomenon of the needle arising when the needle collides against the fixed core or the like during valve opening is stopped before the needle reaches a valve closed position for each fuel injection device of each cylinder and to correct the injection quantity of fuel individually and as a detection technology for this purpose, a fuel injection control device disclosed by PTL 2 is known as a means of detecting the collision time of the needle and the fixed core when the fuel injection device finishes valve opening. In PTL 2, the collision timing of the needle and the fixed core when the fuel injection device finishes valve opening by focusing on a phenomenon in which a magnetic material constituting a magnetic circuit is magnetically saturated by a rapidly reducing air gap between the needle and the fixed core and the inductance of the magnetic circuit changes and detecting the timing when the second differential value of the current changes from negative to positive.
PTL 3 discloses a detector of acceleration and the like that detects a movable magnetic body moving in accordance with acceleration of a needle by a differential transformer transducer and generates output in accordance with a displacement of the magnetic body on the secondary side of the transformer transducer, wherein a linear voltage is obtained in accordance with acceleration by providing in series a solenoid that adds a voltage induced by the magnetic flux of a primary solenoid to the output of a secondary solenoid in phase or reverse movement.